1. Field of the Invention
This invention relates to damper assemblies for installation within conventional air ducts to control airflow therethrough; and more particularly, the present invention relates to damper assemblies of the opposed blade type having a plurality of blades.
2. Prior Art
Damper assemblies for controlling airflow through a duct are well known and have achieved common use in most heating, airconditioning and ventilating systems installed in residences and commercial buildings. Typically, these damper assemblies comprise a frame structure adapted to be fitted to the end of a duct, defining a generally rectangular opening. The frame supports a plurality of damper blades which are pivotally mounted in the frame and move between open and closed positions, wherein a minimum of resistance to airflow is present when in the open position and airflow is blocked with substantially no leakage when in the closed position.
Blade type damper assemblies in the prior art have utilized blades fabricated from strips of metal, extruded metal, molded plastic, and a combination of metal and plastic. Prior art damper assemblies have taken on many configurations, but all have involved the assemblage in a frame of a set of controllable blades. Prior art damper assemblies having a plurality of controllable blades assembled in a set and supported in a frame have generally required a large number of individual parts which must be put together. The procedure of assembling numerous individual parts that comprise the blade support portion and the interconnecting control linkage portion is quite costly, thus making damper assemblies of that type quite expensive.
Damper assemblies of metal are the most prevalent in current use because of the relative low cost of metal dampers, by virtue of the simplicity and inexpensiveness of the machinery and equipment necessary to form the component parts. Metal dampers do, however, require a substantial amount of maintenance after installation, as they are subject to rusting and must be painted.
Plastic damper assemblies, while not being subject to the maintenance required for metal dampers, has the disadvantage of being more costly to fabricate. The injection molding machines and dies necessary to form the component parts are more expensive than the equipment for forming comparable metal parts, escalating the overall cost of the damper assembly. Thus, in order for plastic dampers to be cost competitive with metal dampers, the expensive procedure of assembling several component parts must be at least substantially eliminated.
Representative of the prior art damper assemblies is that disclosed in Scharres, U.S. Pat. No. 3,084,715. In the damper assembly disclosed there, the damper blades are formed by extruding material in a plastic state through a suitable die to form blades that are rectangular in shape and have a slot formed in the cross section of each end for receiving a stiffening member which comprises a stamped metal piece dimensioned to fit within the slot. The damper blades are pivotally supported in a rectangular frame. The mounting technique utilized to support the damper blades within the frame calls for the stiffening member to be formed with tangs projecting at each end. Fitted to each of the tangs is a shaft having an axial passage shaped to receive the tang, effecting a nonrotatable connection between the shaft and the damper blade. The shafts at the opposite ends of the damper blade are journaled in bearings supported on the side members of the frame structure, which frame members are apertured to receive the bearings. The bearings are a tubular sleeve of nylon or metal dimensioned to extend through aligned apertures in opposed frame members. A collar is utilized to retain the bearing in place in the assembly. In addition to the foregoing parts that must be assembled to mount the damper blades in the frame, it is also required that a linkage be attached to the assembly for coupling the damper blades together. A suitable linkage is disclosed in the patent for rotating the damper blades comprises a series of rigid links connecting the free ends of crank arms which are affixed to each damper blade. Alternatively, adjacent damper blades of the assembly could be coupled together by intermeshing gears mounted on the damper blade shafts.
Another damper assembly illustrative of prior art damper assemblies utilizing several individual parts to support the damper blades in a frame is that of McQuown, U.S. Pat. No. 3,176,715. The damper disclosed in McQuown is constucted of aluminum, with each blade being equipped at each end with a rotary bearing that is journaled in a circular opening in a side member of the frame. The rotary bearings are molded of plastic and include a hollow axial bearing stub that is rotatably journaled in the frame side member and a disc portion having external peripheral gear teeth. Each rotary bearing has inwardly projecting ribs provided on the disc portion, which ribs define a groove like mounting socket of the same size and configuration as the damper blade end to permit direct mounting of each blade between an aligned pair of rotary bearings. The disc portions of the rotary bearings are arranged with their gear teeth interlocking so that all damper blades rotate simultaneously from one position to another.
One attempt to provide a damper assembly having a plurality of damper blades, but which avoids the necessity of assembling several individual parts to form the complete mechanism is that of Eberhart, U.S. Pat. No. 3,301,164. Eberhart seeks to provide a low cost damper assembly by molding in a single operation an entire damper assembly having a plurality of movable vane members in a supporting framework with interconnecting control linkage. Thus, Eberhart's solution is to simultaneously form and mold as a single piece of plastic material the entire damper assembly. The movable vane are connected to the supporting framework by integrally molded flexible web portions to render the vanes movable on the frame. Also, a coupling linkage is provided by an integrally molded gang bar that is connected to a side edge of each vane by a flexible web portion, such that a reciprocating movement of the gang bar will cause a simultaneous pivotal movement of the interconnected vanes.
Another approach to obviating the costliness of damper assemblies having many individual parts that must be welded or otherwise joined together to form the damper assembly is that of Dry, U.S. Pat. No. 3,500,739. The damper assembly in Dry is a one-piece frame formed by injection molding in a die, with parts to be added to the frame to complete the assembly also being formed by injection molding in a die. More specifically, the damper assembly in Dry comprises a plastic L-shape frame having a series of U-shaped slots along the edge of the sides of the frame equally spaced from each other. A plurality of damper blades extend across the frame; the shutter blades having pin extensions for mating with the U-shaped slots on the frame. An extension projects from an end of each of the damper blades, with a lever engaging each of the extensions to provide simultaneous rotation of the blades between open and closed positions.
Accordingly, prior to the development of the present invention, there has been no plastic damper assembly for use in various types of airflow distribution systems, which is of simple construction employing only a few easy-to-assemble parts that may be put together without resort to an extensive assembly procedure, and which will be low in cost. Therefore, the art has sought an inexpensive, easy-to-assemble damper assembly absent the problems of previously proposed damper assemblies.